JPH04372563A - Linear direct current motor and image scanner using this motor - Google Patents

Abstract

PURPOSE:To grasp the moving speed of a moving element by making the constitution simple and cheap, and lengthenable. CONSTITUTION:Field magnets having N- and S- magnetic poles alternately in the longitudinal direction and an armature having more than one group of driving armature coils facing these field magnets are provided. Either the said field magnets or armature is made a moving element 1 and the remainder a stator 2 to produce a linear direct current motor. A displacement sensor 14 is fitted to the moving element 1, and a sensor target 15 having a cyclic shape of protrusions and recessions is provided on a stator 2 in the moving direction on a locus facing this displacement sensor 14. The speed of the moving element 1 is calculated by a calculating means, on the basis of the cycle of the protrusions and recessions of this sensor target 15 detected by the displacement sensor 14.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear DC motor and an image scanner using this motor.

0002

2. Description of the Related Art Generally, a linear DC motor is used as a drive source for linearly moving an optical head, an image scanner, or the like. In other words, it is possible to use a rotary motor and convert it into linear motion using a transmission system, but with such a drive system, there is a limit to the high accuracy of feed due to play and backlash caused by the transmission system. .

[0003] Japanese Patent Laid-Open No. 122357/1983 discloses a linear DC motor equipped with an optical linear encoder for the purpose of highly accurate movement and stopping. This allows the position and propulsion speed of the movable element to be easily detected by reflecting the light from the optical wavelength generating element on an inclined reflecting surface provided on the side of the movable element and receiving it with the optical wavelength receiving element. It is something. According to this, the position and propulsion speed can be easily detected, making it possible to move or stop with high precision.At the same time, since there is no need to move the optical wavelength generating element and the optical wavelength receiving element together with the movable element, the power cord It has the advantage that it does not get in the way.

0004

[Problems to be Solved by the Invention] However, according to such a conventional method, it is necessary to use expensive optical components such as an optical wavelength generating element, an inclined reflection surface, an optical wavelength receiving element, etc. It also requires highly accurate assembly and adjustment, making it troublesome to handle.

[0005]

[Means for Solving the Problems] A field magnet having magnetic poles of N and S poles alternately in the longitudinal direction, and an armature having one or more drive armature coil groups facing the field magnet. In a linear DC motor in which one of the field magnet and the armature is a movable element and the other is a stator, a displacement sensor is attached to the movable element, and a displacement sensor is mounted opposite to the displacement sensor. A sensor target formed in a periodic uneven shape in the moving direction on a locus of movement is provided on the stator, and calculation means is provided for calculating the speed of the movable element based on the uneven period of the sensor target detected by the displacement sensor. Ta.

In the invention as claimed in claim 2, a sensor whose output changes according to the target area is attached to the movable element, and the sensor is formed in a pattern whose area changes periodically in the direction of movement on a locus facing the sensor. A target was provided on the stator, and calculation means was provided for calculating the speed of the movable element based on the pattern period of the sensor target detected by the sensor.

In the third aspect of the invention, such a linear DC motor is used in an image scanner, and a reading optical system member is mounted thereon as a movable member for sub-scanning.

[0008]

[Operation] According to the invention as claimed in claim 1, there is provided a displacement sensor attached to the movable element, and a sensor target positioned on the movement locus of the displacement sensor and provided on the stator side and having a periodic uneven shape. By measuring the period of irregularities and calculating the speed of the mover, the function of the linear encoder is ensured, and high-sensitivity speed detection is possible with an inexpensive and simple configuration. Operation control becomes possible. In particular, the sensor target may be long and has fewer restrictions.

The same applies to the case according to the invention as claimed in claim 2, in which a sensor is attached to the movable element and the output changes depending on the target area, and a sensor is installed on the stator side and positioned on the movement locus of this sensor. In combination with a sensor target whose pattern changes periodically, the function of a linear encoder is ensured by measuring the pattern period and calculating the speed of the mover, making it possible to achieve high-sensitivity speed with an inexpensive and simple configuration. Detection is possible, and highly accurate operation control of the movable element is possible. In particular, the sensor target may be long and has fewer restrictions.

According to the third aspect of the invention, by using such a linear DC motor as a sub-scanning drive source in an image scanner, stable speed control can be performed, and highly accurate reading can be performed at low cost. In particular, it is possible to increase the length, and it is also possible to read large sizes.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. 1 to 7. First, the linear DC motor of this embodiment uses the armature as the mover and the field magnet as the stator 2.

The movable element 1 includes a movable back yoke 3, a coil substrate 4 attached to the movable back yoke 3, shafts 5 fixed to four corners on both sides of the movable back yoke 3, and a rotatable member rotatable on each shaft 5. It is composed of an attached roller 6, an armature coil group consisting of coils 7 fixed to the coil substrate 4 and continuously arranged along the longitudinal direction of the substrate, and a Hall element 8 for position detection. .

The stator 2 also includes a long base plate 10 having a stepped or groove-shaped rail portion 9 for guiding the rolling of the roller 6, and a fixed back yoke 11 fixed on the base plate 10. and a permanent magnet consisting of magnetic poles 12 provided on the fixed back yoke 11 and magnetized alternately as north and south poles.

In such a basic configuration, there is always a constant gap between the magnetic pole 12 and the coil 7, and the coil 7 and the Hall element 8 are connected to each other via the connector 13 attached to the coil board 4. It is connected to a control device described later.

In this embodiment, a displacement sensor 14 is attached to a part of the movable element 1 in a manner that it projects laterally. The displacement sensor 14 is a non-contact type, for example, an eddy current displacement meter, but it may also be one that uses light, sound, or magnetism. A sensor target 15 is provided on the base plate 10 along the movement trajectory of the displacement sensor 14. This sensor target 15 has a sinusoidal periodic uneven pattern formed along the moving direction of the movable element 1 on the opposing surface 15a facing the displacement sensor 14. The uneven pattern on the facing surface 15a of the sensor target 15 is not limited to a sine wave shape, but may also be a rectangular wave shape, etc.
Any uneven pattern may be used as long as the distance from the displacement sensor 14 increases or decreases periodically. The detection output of the displacement sensor 14 is also input to a control device, which will be described later, via the connector 13, and is used as a feedback control signal.

Next, the configuration of the control device will be explained with reference to FIG. Basically, microprocessor 16, RAM 17
A command generating device 21 is connected to such a microcomputer 19 via a bus 20. This command generation device 21 generates state command signals such as a position command signal and a speed command signal for commanding the state of the movable element 1. The motor drive device 22 also responds to the output signal of the Hall element 8 and the output signal from the program-controlled microcomputer 19.
General 3-phase motor drive IC23 that outputs signals to
is provided. Through such drive control, the movable element 1 moves at a speed commanded by the command generating device 21. The output of the displacement sensor 14 at this time is the output of the waveform shaping circuit 24.
, the microcomputer 19 determines the speed of the movable element 1 via the detection interface device 25 serving as a calculation means.
be taken into account.

For example, the output of the displacement sensor 14 shown in (a) in FIG. 4 is waveform-shaped by the waveform shaping circuit 24 to become a rectangular wave as shown in (b) in the same figure. That is, this waveform shaping circuit 24 has a function of converting a sine wave input into a rectangular wave output. Therefore, if the concavo-convex pattern shape of the facing surface 15a is a rectangular waveform, this waveform shaping circuit 24 is not necessary, and the output of the displacement sensor 14 may be input directly to the detection interface device 25.

Next, a method for detecting the speed of the movable element 1, that is, a function of the detection interface device 25 will be explained. This detection interface device 25 outputs the output of the displacement sensor 14, which has been shaped into a rectangular wave by the waveform shaping circuit 24, to an interrupt terminal of the microprocessor 16.
It is equipped with a counter that counts the reference clock CLK.

Now, in FIG. 5, the state immediately before the edge E1 of the output OB of the waveform shaping circuit 24 arrives will be explained. A counter built into the detection interface device 25 calculates the pulse period of Tn-1 of the output OB using the reference clock CLK.
A count number given based on (for example, 0FFFFH)
Decrement count from. When edge E1 reaches the microprocessor 16 interrupt, the interrupt routine shown in FIG. 6 is executed. Then, the decremented count value of the counter is latched in the storage register built into the detection interface circuit 25 (counter latching). Then, the latched decrement count value is stored in the RAM 17. Then, the initial count value (0FFFFH) for counting the pulse period of Tn
is given, the decrement count is started again, and the interrupt processing is finished. When edge E2 reaches the interrupt again, the above-described process is repeated in the same way.

At this time, the moving speed v of the movable element 1 is determined by equation (1). However, TCLK: CLK period,
NE: number of output pulses of the waveform shaping circuit 24 per unit length; n: number of CLK counts (=OFFFFH−number of decrement counts).

[0021]

[Equation 1] v=(1/NE)・{1/(TCLK・n)}
(1) The speed information of the movable element 1 obtained in this way is used for feedback control. For example, consider an example in which proportional control, which is commonly used, is applied to speed control. As described above, the moving speed of the movable element 1 is determined as a digital value and is input into the microcomputer 19. In proportional control, the control voltage to the linear DC motor is generally expressed by equation (2).

[0022]

[Formula 2] V=R(Fr/KF)+K(Rv-v)
……………(2) Here, V: control voltage, R: coil resistance, K: proportional gain, v: mover speed, KF: thrust constant, Fr: friction force.

In equation (2), R, Fr, and KF are values unique to the motor, and K, K', and K'' are design values for the control system, so they are all known constants. This is a set value, and v is obtained as described above, so in advance (
2) By inputting the equation and the above-mentioned constants into the ROM 18 in the microcomputer 19 as a program or a list, the voltage V required for control can be easily determined by calculating the equation. Furthermore, the actually obtained control voltage V is pulse-modulated within the microcomputer 19 and output to the three-phase motor drive IC 23 to perform so-called PWM control.

By the way, as shown in FIG. 7, such a linear DC motor is used, for example, as a sub-scanning drive source for a reading optical system member of an image scanner 26. Figure 7
An image scanner 26 shown in FIG. 2 exposes a document 28 placed on a contact glass 27 to a slit using an exposure lamp 29 such as a fluorescent lamp or a halogen lamp and a reflector 30, and directs the reflected light to an imaging element such as a SELFOC lens. 31
These reading optical system members 29 to 32 are fixedly mounted on the movable member 1 as a reading unit 33 to sub-scan the surface of the document 28. It is configured. The stator 2 is fixed to a housing 34 of the image scanner 26.

In such a configuration, the reading unit 33 reads the image of the original 28 in the main scanning direction by self-scanning while being sub-scanned by the linear DC motor (mover 1), and reads the original image as a whole two-dimensionally. . Here, since the reading unit 33 uses the above-mentioned direct drive linear DC motor for driving in the sub-scanning direction, it is possible to perform drive control at low cost and without speed fluctuations caused by play or backlash in the transmission system, and to achieve high performance. Accurate reading is possible.

Next, a second embodiment of the present invention will be explained with reference to FIGS. 8 to 11. In this embodiment, first, instead of the displacement sensor 14, a sensor 35 whose output changes depending on the target area is attached to the movable element 1. A sensor target 36 is provided on the base plate 10 so as to face the movement trajectory of the sensor 35. In this sensor target 36, the shaded part in FIG. 8 becomes the sensing part of the sensor 35, and as shown in the figure, it is formed into a triangular pattern whose area changes periodically in the moving direction of the movable element 1. It is formed. However, the pattern shape of the sensor target 36 is not limited to a triangular shape, but may be any shape whose area changes periodically. The sensor 35 and the sensor target 36 can be combined in this way, for example, by applying light and measuring the level of the reflected light with a detector. Therefore, for example, the sensor 35 may be composed of a light source and a detector.

Even with such a configuration, the control system may be constructed in the same manner as shown in FIG. 3 by replacing the displacement sensor 14 with the sensor 35. In this case, sensor 3
The output signal from 5 has a triangular sawtooth shape as shown in FIG. 10(a), and is waveform-shaped by the waveform shaping circuit 24 to become a rectangular wave output as shown in FIG. 10(b). Therefore, the moving speed of the movable element 1 can be detected and controlled in the same manner as in the embodiment described above.

This embodiment can also be applied to the image scanner 26 as shown in FIG. 11, as in the case of FIG.

[0029]

Effects of the Invention Since the present invention is constructed as described above, according to the invention set forth in claim 1, the displacement sensor attached to the movable element and the displacement sensor positioned on the movement locus of the displacement sensor on the stator side According to the invention as claimed in claim 2, the speed of the movable element is calculated by measuring the period of irregularities in combination with a sensor target provided in a sensor target having a periodic irregular shape. The pattern period is measured by combining a sensor whose output changes depending on the target area, and a sensor target whose area changes periodically and is placed on the stator side and placed on the movement trajectory of this sensor. By calculating the speed of the mover using control can be performed, and the length of the linear motor can be increased.

Further, in the invention as claimed in claim 3, since such a linear DC motor is used as a sub-scanning drive source in an image scanner, high-precision reading can be performed at low cost, and the length can be increased. This makes it possible to provide an image scanner that can handle large-sized documents.

[Brief explanation of drawings]

FIG. 1 shows a first embodiment of the present invention, in which (a) is a front view and (b) is a side view.

FIG. 2 is a plan view.

FIG. 3 is a block diagram showing a control system.

FIG. 4 is a timing chart showing signal waveforms.

FIG. 5 is a timing chart showing signal waveforms.

FIG. 6 is a flowchart.

[Figure 7] This shows an example of application to an image scanner.
A) is a front view, and (b) is a side view.

FIG. 8 shows a second embodiment of the present invention, in which (a) is a front view and (b) is a side view.

FIG. 9 is a plan view.

FIG. 10 is a timing chart showing signal waveforms.

FIG. 11 shows an example of application to an image scanner.
(a) is a front view, and (b) is a side view.

[Explanation of symbols]

1 Mover = Armature 2 Stator = Field magnet 14 Displacement sensors 15, 36 Sensor target 25 Calculation means 26 Image scanner 35 Sensor

Claims (3)

[Claims] 1. A field magnet having magnetic poles of N and S poles alternately in the longitudinal direction, and an armature having one or more drive armature coil groups facing this field magnet, and these In a linear DC motor in which one of the field magnet and armature is a mover and the other is a stator,
A displacement sensor is attached to the movable element, and a sensor target formed in a periodic uneven shape in the direction of movement is provided on the locus opposite to the displacement sensor, and the unevenness of the sensor target detected by the displacement sensor is provided on the stator. A linear DC motor characterized in that a calculation means for calculating the speed of the movable element based on a period is provided. 2. A field magnet having magnetic poles of N and S poles alternately in the longitudinal direction, and an armature having one or more drive armature coil groups facing this field magnet, and these In a linear DC motor in which one of the field magnet and armature is a mover and the other is a stator,
A sensor whose output changes according to the target area is attached to the movable element, and a sensor target formed in a pattern whose area changes periodically in the movement direction on a locus opposite to the sensor is attached to the stator, and the sensor A linear DC motor characterized in that a calculation means is provided for calculating the speed of the movable element based on the pattern period of the sensor target detected by the sensor target. 3. An image scanner using a linear DC motor according to claim 1, wherein the movable element is mounted with a reading optical system member and performs sub-scanning.